The present invention relates to a color overhead projector which reads an image from a color document, writes the read image onto a film, and project the image onto a screen by illumining the film.
Applicants have proposed an overhead projector which writes the image read from a document onto a thermochromic film and projects the image onto a screen by causing light to transmit through the film (Japanese Patent Application No. 309334/1986).
The thermochromic film has the characteristic that it becomes optically transparent when it is heated to a first temperature, for example, of about 60.degree. C., maintains its transparent state even if it returns to normal temperature, becomes opaque when it is heated to a second temperature, for example, of 72.degree. C., and it maintains its opaqueness even if it is returns to its normal temperature. Therefore, if the whole film on which an image is already formed is heated to the first temperature (transparentizing temperature), the image will disappear. If the transparentized film in which the image has disappeared is heated to the second temperature selectively in accordance with the image in the original document, a new image will be formed.
Therefore, it is possible to use the same film repeatedly.
However, as described above, the image formed on a thermochromic film is composed of transparent and opaque portions, so that only a monochromatic or black and white image can be obtained on the screen.